Mastering aluminum machining: Achieving process reliability and efficiency with the right coolant

Aluminum shapes key industries from aerospace and automotive to medical technology as a lightweight, strong, and easily machinable material. However, machining aluminum in production places high demands on machines, tooling, and coolants. This article analyzes the five core challenges of aluminum machining, explains their causes and consequences, and shows you a field-proven solution path: Systematic process optimization combined with the high-performance coolant rhenus TY 155 L.

Whether drilling, turning, or milling – the machining of aluminum is a demanding process in the metalworking industry. Aluminum is lightweight, easily machined, and thanks to its versatility, an indispensable material for key industries – from aerospace and automotive to medical technology. But these advantages come at a price: In machining, aluminum places very specific demands on processes, machines, and operating materials. Its high thermal conductivity, tendency towards built-up edge formation, and sensitive surfaces make it a material that is unforgiving of errors.

For production managers, this means: Successfully machining aluminum requires not only precision in tooling and machinery but also a well-thought-out strategy. Even minor weaknesses in cooling and lubrication behavior directly impact dimensional accuracy, tool life, and surface quality – and thus the efficiency and cost structure of production.

Although aluminum is considered easily machinable, its properties lead to recurring phenomena under insufficient process control. These compromise quality and economic efficiency. Five key aspects are:

Challenge 1: Built-up edge (BUE) formation in aluminum – causes and effects

What exactly is a built-up edge?
During built-up edge formation, machined aluminum material adheres to the tool’s cutting edge. An additional, unstable “edge” of compacted material forms, which grows and breaks off uncontrollably. This phenomenon impacts process stability.

Why aluminum tends to form built-up edges:
The high affinity of aluminum for cold welding is a central factor responsible for this. Under the high pressure and the temperatures occurring at the cutting edge, adhesive forces develop between the tool and workpiece material. An inadequate or unstable coolant additive package cannot effectively prevent this adhesion. Particularly softer, low-alloy, or long-chipping aluminum types are highly prone to this effect due to their ductility and the often continuous chip formation, as the lack of chip breaking additionally increases contact time and friction at the cutting edge.

Effects on precision, surface, and tool:
The direct consequences of built-up edge formation are severe and include dimensional deviations due to the unstable geometry of the built-up edge, reduced surface quality due to break-offs causing grooves, as well as significantly shortened tool life due to rapid abrasive wear.

The role of the coolant: Lubrication against adhesion:
A high-performance coolant like rhenus TY 155 L prevents built-up edges through its excellent lubricating properties. Special additives effectively reduce friction and the tendency for adhesion, thereby suppressing cold welding.

Challenge 2: Staining on aluminum – causes and prevention

Appearance and impact of surface stains:
Dull spots, streaks, water spots, or localized discoloration on the machined aluminum surface represent a significant visual defect. They are particularly critical on appearance parts and can lead to the rejection of the entire component.

Coolant-related causes for staining:
The causes for this are diverse and often found within the coolant itself. These include, firstly, unstable emulsions that create local differences in surface chemistry through uneven additive distribution or uneven wetting. Secondly, unsuitable additives (such as aggressive corrosion inhibitors or certain emulsifiers) can react chemically with the aluminum surface. Thirdly, unfavorable residue or drying behavior leads to visible deposits or uneven drying. Fourthly, pH value deviations can also attack the sensitive aluminum surface.

Consequences for quality and further processing:
The results are often scrap or costly rework. Additionally, stains can negatively affect subsequent processes such as anodizing, painting, or bonding and are a frequent reason for quality defects.

Coolant properties for stain-free results:
An optimized coolant like rhenus TY 155 L ensures stain-free surfaces through a combination of important properties: high stability, selected material-compatible additives, a suitable pH value, as well as optimized residue and drying behavior.

Challenge 3: Corrosion on aluminum components – causes and protective measures

Corrosion risks with aluminum:
Despite its natural oxide layer, aluminum is susceptible to certain types of corrosion such as white rust or contact corrosion. Triggers are often coolants unsuitable for the process or unfavorable storage conditions.

How coolants can promote corrosion:
Several factors in the coolant can promote corrosion: pH instability, where the value drifts into critical ranges, attacks the oxide layer. Aggressive ingredients such as high chloride or sulfate content or unsuitable biocides can also be corrosive. Furthermore, electrochemical (contact) corrosion can occur through contact with nobler metals in the coolant system. Finally, insufficient temporary corrosion protection from the coolant during intermediate storage can also lead to problems.

Effects of corrosion:
The consequences range from visual impairments such as white rust to functional problems due to altered surface structure, and in extreme cases, weakening of the material.

Corrosion protection through the right coolant:
rhenus TY 155 L prevents corrosion through targeted measures: The formulation ensures pH stability in the optimal range, avoids corrosion-promoting components, and utilizes a synergistic inhibitor package to protect the aluminum surface. Good filterability also helps remove corrosion-promoting particles.

Challenge 4: Foam formation in coolant – background and consequences

When and why foam occurs:
Excessive foam formation is a common problem with internal coolant supply at high pressures or high turbulence in the coolant system. The emulsifiers and surfactants contained in the coolant tend to form stable foam under shear stress or air entrainment. This is often exacerbated by factors such as soft water, high coolant concentration, unfavorable system design, or contaminants.

Negative effects of foam in the process:
The consequences of heavy foaming are diverse: It reduces cooling and lubricating performance, can block sensors, lead to overflowing tanks or even machine downtime, and cause quality problems due to uneven cooling.

Coolant formulation against foam:
rhenus TY 155 L is designed as an excellent low-foaming and air-release formulation. Special, low-foaming systems quickly release entrained air and prevent the formation of stable foam, which ensures process reliability even under demanding conditions.

Challenge 5: Effective chip management in aluminum machining

The challenge of aluminum chips:
Aluminum often generates large chip volumes. The chips are frequently long, tough, and tend to tangle, which complicates removal from the machining zone and the machine.

Causes of unfavorable chip behavior:
The low hardness and high toughness of many aluminum alloys make short chip breaking difficult. This is exacerbated by unsuitable tool geometries, inappropriate cutting parameters, or insufficient cooling and lubrication. The long chips can then wrap around tools or block conveyor systems.

Consequences of inadequate chip management:
This often leads to machine downtime due to blocked chip conveyors, can cause surface damage from dragged chips, impair cooling and lubrication at the cutting edge, and requires significant cleaning effort.

How the coolant supports chip management:
An appropriate coolant significantly supports chip management, although it only has a limited influence on chip breaking. rhenus TY 155 L ensures effective chip removal through its high flushing effect, enabled by optimized viscosity and wetting properties. Its good filterability also allows for efficient cleaning of the coolant. Supplementary process-related measures to promote controlled chip breaking remain important.

The described phenomena often reinforce each other. Reduced tool life increases costs and downtime. Quality problems increase scrap and rework. Process instabilities reduce Overall Equipment Effectiveness. Ultimately, inadequately controlled aluminum processes lead to higher unit costs and reduced competitiveness. The coolant choice is therefore a strategic decision with a direct impact on the bottom line.

Master the challenges through a two-step approach: Optimize process parameters and select the appropriate coolant.

Factor 1: Holistically analyze and optimize the machining process

Importance of Analysis:
Before specific measures such as coolant selection are taken, a strategic assessment of the entire machining system is essential. Optimization potential often lies in the complex interactions of individual components.

Specific Areas of Analysis:
For maximum process reliability with aluminum, evaluating the complex interactions is crucial. Validate the coordination between the specific alloy and the employed tooling technology, including the selected process parameters. Critically assess the dynamic system rigidity of the machine and clamping setup. Finally, ensure consistently optimized coolant management – from supply and condition monitoring to filtration and water quality.

Goal of Analysis:
A stable, reproducible process through optimally coordinated components.

Factor 2: Understanding the specific requirements for an aluminum coolant

Central Role of the Coolant:
The coolant is multifunctional in aluminum machining. An unsuitable formulation exacerbates problems. Selection requires specific performance criteria.

Detailed Coolant Requirements for Aluminum:
A high-performance coolant for aluminum must combine the following properties: